Analgesia produced by injection of lidocaine into the anterior cingulum bundle of the rat

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Abstract
The role of cingulum in the perception of tonic and phasic pain was examined by injecting lidocaine, a local anesthetic, into the anterior cingulum bundle of the rat. A cannula was stereotaxically implanted into the anterior cingulum on one side in anesthetized rats. Seven to 10 days after surgery, the rats were infused with 1 μl of 2% lidocaine in saline or saline alone into the anterior cingulum bundle immediately prior to testing for analgesia in the formalin or foot-flick test. Injection of lidocaine into the anterior cingulum bundle produced a significant reduction in formalin pain scores, but had no effect on foot-flick latencies. The analgesia in the formalin test persisted for the entire 40 min observation period. No analgesia in the formalin test was observed in rats that received injections of saline into the cingulum, lidocaine into the cingulum 90 min prior to testing or lidocaine into the cingulate cortex. These data suggest that the cingulum is involved in the perception of tonic pain but not phasic pain, and support previous studies which indicate that different neural mechanisms underlie different types of pain. Furthermore, these findings suggest that the cingulum is involved in the affective component of pain and that interruption of cingulum activity with lidocaine can produce analgesia.